The present invention relates generally to communication over wireless channels, and more particularly, to antennas for communicating over wireless channels.
Multiple-antenna communication, where multiple antennas are used for transmitters or receivers or both, has become popular because this type of communication can increase efficiency. In this context, xe2x80x9cefficiencyxe2x80x9d usually refers to xe2x80x9cspectral efficiency,xe2x80x9d a term describing how many bits can be communicated within a given bandwidth.
Multiple-antenna communication can take advantage of complex scattering environments. In such an environment, signals transmitted from one location can take many different paths before reaching a receiver with multiple antennas. Each antenna of the receiver effectively receives different copies of the same signals, because of the different paths the signals take to each antenna. Due to these multiple paths, a multiple-antenna system can use the different copies to reduce errors or increase transmitted information, both of which result in more efficiency.
Nonetheless, a multiple-antenna system can be complex to implement and can take relatively large amounts of space. This is particularly disadvantageous for those applications where smaller antennas are desired. A need therefore exists for techniques that enable and create smaller antennas that improve communication efficiency.
Aspects of the present invention provide compact antennas, communication units having the same and methods for designing the same. The compact antennas are adapted to emit one or more directed beams, with each directed beam having one or more degrees of freedom per concentration region in the directed beam.
In an aspect of the invention, a compact antenna is disclosed comprising one or more input feeds and one or more sets of elements. Each set of elements is coupled to one or more of the input feeds, and each set of elements has a property that input signals applied to input feeds coupled to the set of elements causes a directed beam to be emitted. A directed beam is a radiation pattern in which power is concentrated in a concentration region. A concentration region may be, for instance, a solid angle. Each element of the set or sets of elements has a largest dimension. At least a given element of a set of elements has a largest dimension smaller than a smallest wavelength to be emitted from the antenna. Additionally, the antenna is adapted to simultaneously transmit the input signals. Usually, more than two input signals are transmitted simultaneously. When a concentration region is large enough, more than one degree of freedom can be contained in the concentration region, meaning that more than one independent input signal may be emitted via the directed beam having the concentration region.
In another aspect of the invention, a communication unit comprises the antenna and signal processing circuitry. The signal processing circuitry comprises reception circuitry, transmission circuitry, or both. Illustratively, for transmission, multiple input signals can be combined and coupled to the one or more feeds of the antenna.
In yet another aspect of the invention, techniques for designing a compact antenna are presented. Such techniques include selecting a concentration region to be emitted from the antenna, where the concentration region is to be emitted in a directed beam. Concentration for the selected concentration region is determined and increased until the concentration reaches a predetermined concentration. Antenna geometry is defined in order to create the concentration region with the predetermined concentration. The step of defining creates one or more sets of elements and one or more input feeds.
Illustratively, one technique for designing a compact antenna then comprises determining multipole coefficients corresponding to the predetermined concentration, determining currents corresponding to the multipole coefficients, and determining antenna geometry suitable for creating the currents.
A more complete understanding of the present invention, as well as further features and advantages of the present invention, will be obtained by reference to the following detailed description and drawings.